Extreme ultraviolet coherent diffraction tomographic imaging method based on random phase modulation

Abstract

The application discloses an extreme ultraviolet coherent diffraction stack imaging method based on random phase modulation, which is realized through an extreme ultraviolet phase modulation stack imaging light path of a random phase plate. The imaging light path comprises a high harmonic light source, a pinhole, a phase plate and a photoelectric coupling detector. The high harmonic light source emits light to irradiate a probe. A sample to be measured is arranged between the pinhole and the phase plate. The phase plate is used for phase modulation. The light irradiated by the probe is irradiated onto the sample to be measured through the pinhole, propagates a preset distance, and then reaches the plane of the photoelectric coupling detector through the phase plate. The diffraction pattern of the sample to be measured is obtained. Iterative processing is performed on the first amplitude information of the emergent light, the second amplitude information of the reverse propagation, the first diffraction pattern light field and the first diffraction pattern light spot. The best sample to be measured pattern is obtained, and the best sample to be measured information and the best light irradiation probe information are separated. The method can realize lensless imaging, avoids aberration and aperture limitation caused by the use of a lens, and has a simpler system and lower cost.

Description

Technical Field

[0001] This invention relates to the field of imaging technology, and in particular to an extreme ultraviolet coherent diffraction stacking imaging method based on random phase modulation. Background Technology

[0002] With the rapid development of semiconductor technology, nanoscience, and emerging quantum technologies, modern imaging techniques require nanometer-level three-dimensional resolution. However, since photodetectors can only record intensity information, it is necessary to recover the phase of the sample image. Stacked imaging technology utilizes coherent diffraction patterns to calculate and recover the phase of the sample image, thereby obtaining the three-dimensional structure of the sample. This technology can achieve high resolution without requiring sophisticated, complex, and expensive imaging optics. Summary of the Invention

[0003] To address the shortcomings of existing technologies, this invention provides an extreme ultraviolet coherent diffraction stacked imaging method based on random phase modulation.

[0004] To solve the above-mentioned technical problems, the present invention provides the following technical solution:

[0005] An extreme ultraviolet coherent diffraction stacked imaging method based on random phase modulation is realized through an extreme ultraviolet phase modulation stacked imaging optical path with a random phase plate. The imaging optical path includes a high-order harmonic source, a pinhole, a phase plate, and an optocoupler detector. The high-order harmonic source emits a light probe, and a sample to be tested is placed between the pinhole and the phase plate. The phase plate is used for phase modulation. The light probe illuminates the sample to be tested through the pinhole, and after propagating a preset distance, it passes through the phase plate to the plane of the optocoupler detector to obtain the diffraction pattern of the sample to be tested. The method acquires information about the sample to be tested and information about the light probe, obtains the phase-modulated outgoing light and the first diffraction pattern light field, and obtains the first diffraction pattern light spot without phase modulation.

[0006] The sample information and illumination probe information are initialized;

[0007] Iterative processing is performed using the first amplitude information of the emitted light, the first diffraction pattern light field, and the first diffraction pattern light spot;

[0008] The optimal sample image is obtained, and then the optimal sample information and the optimal illumination probe information are separated.

[0009] As one possible implementation method, the iterative process includes the following steps:

[0010] Calculate the first diffraction pattern light field of the emitted light and the light probe after propagating a preset distance at a specified position on the surface of the sample to be tested, and obtain the first amplitude information and the first phase information of the emitted light, wherein the first diffraction pattern light field is the diffraction pattern light field without phase modulation.

[0011] Obtain the first diffraction pattern spot without phase modulation after propagation over a preset distance, and correct the first diffraction pattern light field according to the first diffraction pattern spot to obtain the second diffraction pattern light field;

[0012] Phase modulation is performed on the second diffraction pattern light field to obtain the third diffraction pattern light field;

[0013] A second diffraction pattern spot with phase modulation is obtained after propagation over a preset distance. The third diffraction pattern light field is then corrected based on the second diffraction pattern spot to obtain a fourth diffraction pattern light field.

[0014] The fourth diffraction pattern light field is propagated in reverse and irradiated onto the surface of the sample to be tested to correct the first amplitude information and obtain the second amplitude information.

[0015] Based on the extended layered imaging algorithm, the illumination probe information and the sample information to be tested are separated by combining the first amplitude information and the second amplitude information to obtain the updated illumination probe information and the updated sample information to be tested.

[0016] Change the specified position and repeat all the above steps to obtain the final sample information and the final illumination probe information, and calculate the error for the specified number of iterations;

[0017] The process is repeated step by step, incrementing sequentially, until the error is less than a preset threshold, at which point the iteration process is complete.

[0018] As one possible implementation, the first amplitude information in the first diffraction pattern light field is replaced while the first phase information remains unchanged to obtain the second diffraction pattern light field.

[0019] As one possible implementation, the first amplitude information of the emitted light is represented as: ψ j =P i O i (rR j Assuming the preset distance is D, the light field of the first diffraction pattern is represented as follows: Where r represents spatial coordinates, Indicates forward propagation, P i Indicates illumination probe information, O i Represents the information of the sample to be tested, R j Indicates the spatial displacement of the illumination probe. This represents the phase shift caused by phase encoding, where j represents the j-th specified position and i represents the i-th specified position;

[0020] The light field of the second diffraction pattern is represented as follows: Among them, I j This represents the first diffraction pattern spot. This represents the phase shift caused by phase encoding, where j represents the j-th specified position and i represents the i-th specified position;

[0021] The light field of the third diffraction pattern is represented as follows: Where φ is the phase shift introduced by phase modulation. This represents the phase shift caused by phase encoding, where j represents the j-th specified position and i represents the i-th specified position;

[0022] The light field of the fourth diffraction pattern is represented as follows: Among them, I' j This is represented as the second diffraction pattern spot. This represents the phase shift caused by phase encoding, where j represents the j-th specified position and i represents the i-th specified position;

[0023] The second amplitude information is: ψ' j =F -1 (E″′ j ,D,φ), where φ is the phase shift introduced by phase modulation, E″′ j Let represent the light field of the fourth diffraction pattern, and j represent the j-th specified position.

[0024] As one possible implementation method, the updated sample information to be tested is represented as follows: The updated illumination probe information is represented as follows: Where, ψ j Represented as the first amplitude information, ψ' j The second amplitude information is represented by r, the spatial coordinates are represented by α, the iterative update coefficient of the self-selected test sample information is represented by β, the iterative update coefficient of the self-selected illumination probe information is represented by j, the j-th specified position is represented by i, and the i-th specified position is represented by α.

[0025] As one possible implementation method, the error is expressed as: Where M represents the number of rows, N represents the number of columns, j represents the j-th specified position, i represents the i-th specified position, and E″ j Represented as the light field of the third diffraction pattern, I' j This is represented as the second diffraction pattern spot.

[0026] In one possible implementation, the phase plate includes a substrate and a molybdenum groove. The substrate is a silicon substrate, and the surface of the silicon substrate is etched with a 0.086-micrometer molybdenum groove that corresponds to phase modulation of the π-phase phase shift of the diffraction pattern.

[0027] As one possible implementation method, the following steps are also included:

[0028] The light probe illuminates the sample to be tested multiple times at a designated location. After propagating a preset distance, the light passes through a phase plate to the detector, where it is received and recorded as a phase-modulated diffraction pattern. The areas between two adjacent illuminations must partially overlap.

[0029] Remove the phase plate, and illuminate the sample to be tested multiple times at the designated position using the light probe. After propagating a preset distance, the light passes through the phase plate to the detector, where it is received and recorded as a diffraction pattern without phase modulation. The areas between two adjacent illuminations must partially overlap.

[0030] This invention, by adopting the above technical solutions, has significant technical effects:

[0031] This invention correlates the information of the diffraction pattern with that of the sample pattern to be tested, enabling high-precision extreme ultraviolet phase modulation stacked imaging, with imaging accuracy far lower than that of traditional coherent diffraction imaging systems.

[0032] This invention achieves lensless imaging by recording the far-field diffraction pattern of the sample under test and reconstructing the amplitude and phase information by combining a phase recovery algorithm. This avoids the aberrations and aperture limitations introduced by using lenses, resulting in a simpler system and lower cost. In addition, it combines phase modulation and scanning diffraction imaging to achieve extreme ultraviolet phase modulation stacked imaging. Attached Figure Description

[0033] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0034] Figure 1 This is a schematic diagram of a system containing a phase plate in the imaging optical path of the present invention;

[0035] Figure 2 This is a schematic diagram of a system without a phase plate in the imaging optical path of the present invention. Detailed Implementation

[0036] The present invention will be further described in detail below with reference to the embodiments. The following embodiments are explanations of the present invention, but the present invention is not limited to the following embodiments.

[0037] Exemplary method:

[0038] An extreme ultraviolet coherent diffraction stacked imaging method based on random phase modulation is implemented through an extreme ultraviolet phase modulation stacked imaging optical path with a random phase plate, as shown in the image. Figure 1 As shown, the system includes a high-order harmonic source, a pinhole, a phase plate, and an optocoupler detector. The high-order harmonic source emits light to illuminate the probe. The sample to be tested is placed between the pinhole and the phase plate. The phase plate is used for phase modulation. The light probe illuminates the sample to be tested through the pinhole, propagates a preset distance, and then passes through the phase plate to the plane of the optocoupler detector, obtaining the diffraction pattern of the sample to be tested. The system acquires information about the sample to be tested and the light probe, obtaining the phase-modulated emitted light and the first diffraction pattern light field, and the first diffraction pattern light spot without phase modulation. The information about the sample to be tested and the light probe are initialized. Iterative processing is performed using the first amplitude information of the emitted light, the second amplitude information of the reverse propagation, the first diffraction pattern light field, and the first diffraction pattern light spot to obtain the optimal sample to be tested pattern. The optimal sample to be tested information and the optimal light probe information are then separated. The optimal sample to be tested information is the reconstructed information of the object under test. The probe information is a byproduct of separating the optimal sample to be tested information. The optimal amplitude information, i.e., the second amplitude information, can be obtained based on the optimal sample image. The first amplitude information and the second amplitude information separate the illumination probe information and the sample information to obtain the updated illumination probe information and the updated sample information.

[0039] This invention maps diffraction patterns to the information of the sample under test, enabling high-precision extreme ultraviolet phase modulation stacked imaging, with imaging accuracy far lower than that of traditional coherent diffraction imaging systems. By recording the far-field diffraction pattern of the sample under test and reconstructing amplitude and phase information using a phase retrieval algorithm, this invention can achieve lensless imaging, avoiding aberrations and aperture limitations introduced by lenses, resulting in a simpler system and lower cost. Furthermore, it combines coherent modulation and scanning diffraction imaging to achieve extreme ultraviolet phase modulation stacked imaging.

[0040] Example 1:

[0041] This paper describes an extreme ultraviolet (EUV) coherent diffraction stacked imaging method based on random phase modulation, implemented through an EUV phase modulation stacked imaging optical path using a random phase plate. A specific embodiment of the imaging optical path is described below. Figure 1 and Figure 2As shown, the system includes a high-harmonic source 1, a pinhole 2, a phase plate 4, and an optocoupler detector 5. The sample 3 to be tested is placed between the pinhole 2 and the phase plate 4. The high-harmonic source 1 emits light to illuminate the probe, which passes through the pinhole 2 and illuminates the sample 3 fixed to the two-dimensional translation stage. After propagating a certain distance, the light travels through the phase plate 4 to the plane of the optocoupler detector 5. The two-dimensional translation stage is moved within the two-dimensional plane to scan the measurement area of ​​the sample 3, ensuring partial overlap between adjacent scans and recording the phase-modulated diffraction pattern. Subsequently, the phase plate 4 is removed between the sample 3 and the detector 5, and the scanning process is repeated, recording the diffraction pattern without phase modulation. Each diffraction pattern corresponds to a specific scanning position, and a series of diffraction patterns corresponding to each scanning position are recorded. The process involves acquiring information about the sample to be tested and the illumination probe, obtaining the phase-modulated outgoing light and the first diffraction pattern light field, and acquiring the first diffraction pattern light spot without phase modulation; initializing the information about the sample to be tested and the illumination probe; iteratively processing the first amplitude information of the outgoing light, the second amplitude information of the reverse propagation, the first diffraction pattern light field, and the first diffraction pattern light spot; obtaining the optimal sample to be tested pattern, and then separating the optimal sample to be tested information and the optimal illumination probe information.

[0042] In practical operation, a light probe is used to scan and illuminate different parts of the sample under test. The areas between two adjacent illuminations must partially overlap, and the diffraction intensity is recorded simultaneously. Through an iterative process, the optimal sample pattern is obtained. Based on the optimal sample pattern, the lost phase information is reconstructed, and finally, the optimal sample information and the optimal light probe information are obtained. Since the photoelectric coupling element detector 5 can only detect the diffraction intensity (i.e., amplitude information) when receiving the diffraction pattern, while the light field contains both amplitude and phase information, in actual experiments, only the diffraction intensity can be recorded, not the phase information. Therefore, this invention can be understood as a phase recovery method that can simultaneously recover the amplitude and phase information of the object when reconstructing the optimal sample information, thereby improving the reconstruction accuracy. The optimal sample information is the reconstructed object information, or the reconstructed object. Based on the optimal sample pattern, the optimal amplitude information, i.e., the second amplitude information, can be obtained. The first and second amplitude information separate the light probe information and the sample information, resulting in updated light probe information and updated sample information.

[0043] Furthermore, this invention incorporates phase modulation: phase modulation is achieved through a phase plate, which includes a substrate and molybdenum grooves. The substrate is a silicon substrate, and the surface of the silicon substrate is etched with molybdenum grooves of 0.086 micrometers, corresponding to phase modulation of the π-phase phase shift of the diffraction pattern. The phase plate pattern is designed and etched, and then placed in front of the optocoupler to achieve phase modulation of the diffraction pattern.

[0044] The overall implementation process is as follows:

[0045] The sample to be tested is illuminated multiple times at a designated location by an illumination probe. After propagating a preset distance, the sample passes through a phase plate to a detector, where it is received and recorded as a phase-modulated diffraction pattern. The areas between two adjacent illuminations must partially overlap.

[0046] Remove the phase plate and illuminate the sample at the designated location multiple times using the light probe. After propagating a preset distance, the light passes through the phase plate to the detector, where it is received and recorded as a diffraction pattern without phase modulation. The areas between two adjacent illuminations must partially overlap.

[0047] Based on the specific calculation formula, the iterative process includes the following steps:

[0048] (1) Calculate the first amplitude information ψ of the emitted light corresponding to the j-th scanning position. j =P i O i (rR j ), and calculate the first diffraction pattern light field after propagation distance D. The first diffraction pattern light field is the diffraction pattern light field without phase modulation. The amplitude and phase of the diffraction pattern without phase modulation are obtained, where r represents the spatial coordinates. Indicates forward propagation, P i and O i These are the corresponding probes and the samples to be tested, respectively.

[0049] (2) Using the first diffraction pattern spot I obtained by corresponding detection without phase modulation j To correct the unmodulated diffraction pattern light field to obtain the second diffraction pattern light field The entire correction process is essentially about replacing the amplitude while keeping the phase unchanged;

[0050] (3) Calculate the light field E′ of the second diffraction pattern. j The third diffraction pattern light field after phase modulation by the phase plate Where φ is the phase shift introduced by the phase plate;

[0051] (4) Using the phase-modulated second diffraction pattern spot I' obtained from the corresponding detection j To correct the phase-modulated diffraction pattern light field to obtain the fourth diffraction pattern light field

[0052] (5) The light field E″′ of the fourth diffraction pattern j The beam propagates backward to the surface of the sample under test, and the corrected second amplitude information ψ′ of the emitted light is obtained. j ;

[0053] (6) Using the extended layered imaging algorithm, the illumination probe information and the sample information are separated by combining the first amplitude information and the second amplitude information to obtain the updated illumination probe information and the updated sample information. The updated illumination probe information is as follows: Updated information on the test samples

[0054] (7) Sequentially change the scanning position (j = j + 1) and repeat steps 1) to 7) to complete one iteration process, reconstruct the final sample pattern and probe pattern, and calculate the error of the k-th iteration.

[0055] (8) Let k = k + 1, and set the initial guess for this iteration to O. i+1 =O' i and P i+1 =P' i ;

[0056] (9) Repeat the iterative calculation process from 1) to 8) until the error function Q is obtained. i It is small enough to complete the iterative process.

[0057] In operation, the imaging optical path of this invention fixes the sample on a two-dimensional translation stage. A high-order harmonic light source emits light to illuminate a probe, which shines through a pinhole onto the sample. After propagating a certain distance, the light travels through a phase plate to the photocoupler plane. The two-dimensional moving platform translates within the two-dimensional plane to scan the sample measurement area, ensuring partial overlap between adjacent scans and recording the phase-modulated diffraction pattern. Subsequently, the phase plate is removed between the sample and the detector, and the scanning process is repeated to record the diffraction pattern without phase modulation. Each diffraction pattern corresponds to a specific scan position. By scanning and recording a series of diffraction patterns corresponding to different scan positions, data for intensity constraints is provided for the iterative process in the subsequent reconstruction algorithm.

[0058] Furthermore, it should be noted that the shapes and names of the parts and components described in the specific embodiments described in this specification may differ. All equivalent or simple variations made to the structure, features, and principles described in this patent concept are included within the protection scope of this patent. Those skilled in the art to which this invention pertains may make various modifications or additions to the described specific embodiments or use similar methods to replace them, as long as they do not depart from the structure of this invention or exceed the scope defined in these claims, they should all fall within the protection scope of this invention.

Claims

1. A method for extreme ultraviolet coherent diffraction stacked imaging based on random phase modulation, characterized in that, The imaging optical path is achieved through an extreme ultraviolet phase modulation stacked imaging optical path with a random phase plate. The imaging optical path includes a high-order harmonic light source, a pinhole, a phase plate, and an optocoupler detector. The high-order harmonic light source emits a light probe. The sample to be tested is placed between the pinhole and the phase plate. The phase plate is used for phase modulation. The light probe illuminates the sample to be tested through the pinhole. After propagating a preset distance, it passes through the phase plate to the plane of the optocoupler detector to obtain the diffraction pattern of the sample to be tested. The sample to be tested information and the light probe information are obtained to obtain the phase-modulated outgoing light and the first diffraction pattern light field, and the first diffraction pattern light spot without phase modulation is obtained. The sample information and illumination probe information are initialized; Iterative processing is performed using the first amplitude information of the emitted light, the first diffraction pattern light field, and the first diffraction pattern light spot; The optimal sample image is obtained, and then the optimal sample information and the optimal illumination probe information are separated. The iterative process includes the following steps: Calculate the first diffraction pattern light field of the emitted light and the light probe after propagating a preset distance at a specified position on the surface of the sample to be tested, and obtain the first amplitude information and the first phase information of the emitted light, wherein the first diffraction pattern light field is the diffraction pattern light field without phase modulation. Obtain the first diffraction pattern spot without phase modulation after propagation over a preset distance, and correct the first diffraction pattern light field according to the first diffraction pattern spot to obtain the second diffraction pattern light field; Phase modulation is performed on the second diffraction pattern light field to obtain the third diffraction pattern light field; A second diffraction pattern spot with phase modulation is obtained after propagation over a preset distance. The third diffraction pattern light field is then corrected based on the second diffraction pattern spot to obtain a fourth diffraction pattern light field. The fourth diffraction pattern light field is propagated in reverse and irradiated onto the surface of the sample to be tested to correct the first amplitude information and obtain the second amplitude information. Based on the extended layered imaging algorithm, the illumination probe information and the sample information to be tested are separated by combining the first amplitude information and the second amplitude information to obtain the updated illumination probe information and the updated sample information to be tested. Change the specified position and repeat all the above steps to obtain the final sample information and the final illumination probe information, and calculate the error for the specified number of iterations; The process is repeated step by step, incrementing sequentially, until the error is less than a preset threshold, at which point the iteration process is complete.

2. The extreme ultraviolet coherent diffraction stacked imaging method based on random phase modulation according to claim 1, characterized in that, The first amplitude information in the first diffraction pattern light field is replaced while the first phase information remains unchanged to obtain the second diffraction pattern light field.

3. The extreme ultraviolet coherent diffraction stacked imaging method based on random phase modulation according to claim 1, characterized in that, The first amplitude information of the emitted light is represented as follows: Assuming the preset distance is D, the light field of the first diffraction pattern is represented as: ,in, Represents spatial coordinates, Indicates positive propagation. Indicates information about the illumination probe. Indicates the information of the sample to be tested. Indicates the spatial displacement of the illumination probe. This indicates the phase shift caused by phase encoding. Indicates the first A specified location, Indicates the first A specified location; The light field of the second diffraction pattern is represented as follows: ,in, This represents the first diffraction pattern spot. This indicates the phase shift caused by phase encoding. Indicates the first A specified location, Indicates the first A specified location; The light field of the third diffraction pattern is represented as follows: ,in, The phase shift introduced by phase modulation, This indicates the phase shift caused by phase encoding. Indicates the first A specified location, Indicates the first A specified location; The light field of the fourth diffraction pattern is represented as follows: ,in, This is represented as the second diffraction pattern spot. This indicates the phase shift caused by phase encoding. Indicates the first A specified location, Indicates the first A specified location; The second amplitude information is: ,in, The phase shift introduced by phase modulation, This represents the light field of the fourth diffraction pattern. Indicates the first A specified location.

4. The extreme ultraviolet coherent diffraction stacked imaging method based on random phase modulation according to claim 1, characterized in that... Therefore, the updated sample information is represented as follows: The updated illumination probe information is represented as follows: ;in, This is represented as the first amplitude information. This is represented as the second amplitude information. Represents spatial coordinates, This represents the iterative update coefficients of the self-selected test sample information. This represents the iterative update coefficient of the self-selected illumination probe information. Indicates the first A specified location, Indicates the first A specified location.

5. The extreme ultraviolet coherent diffraction stacked imaging method based on random phase modulation according to claim 1, characterized in that, The error is expressed as: Where M represents the number of rows and N represents the number of columns. Indicates the first A specified location, Indicates the first A specified location, Represented as the light field of the third diffraction pattern, This is represented as the second diffraction pattern spot.

6. The extreme ultraviolet coherent diffraction stacked imaging method based on random phase modulation according to claim 1, characterized in that, The phase plate includes a substrate and a molybdenum groove. The substrate is a silicon substrate, and the surface of the silicon substrate is etched with a 0.086-micrometer molybdenum groove that corresponds to phase modulation of the π-phase phase shift of the diffraction pattern.

7. The extreme ultraviolet coherent diffraction stacked imaging method based on random phase modulation according to claim 1, characterized in that, It also includes the following steps: The light probe illuminates the sample to be tested multiple times at a designated location. After propagating a preset distance, the light passes through a phase plate to the detector, where it is received and recorded as a phase-modulated diffraction pattern. The areas between two adjacent illuminations must partially overlap. Remove the phase plate, and illuminate the sample to be tested multiple times at the designated position using the light probe. After propagating a preset distance, the light passes through the phase plate to the detector, where it is received and recorded as a diffraction pattern without phase modulation. The areas between two adjacent illuminations must partially overlap.

Images